Method for producing a hollow shaft

ABSTRACT

A method for producing a hollow shaft from a tubular preform by pressure rolling shapes each end of the preform using at least one forming roller. A tubular preform with a round or polygonal cross-section is used, and the preform is held on a workpiece holder in the central tube region during the entire production process until the hollow shaft is completed.

The invention relates to a method for the production of a hollow shaftfrom a tubular preform by means of pressure rolling, wherein the twoends of the preform are shaped using at least one forming roller, ineach instance.

Such a method is known from DE 103 37 929 A1. This document describes amethod for the production of one-piece hollow bodies having profiled endregions, from a preform having a circular tube cross-section, whereinfirst, in a first method step, the preform is elongated in its centerregion. After completion of this elongation step, the preform isinserted into a different workpiece holder and subsequently, in a secondmethod step, at least one end region is elongated, and in a third methodstep, if applicable, this end region is processed further.

However, this known method is relatively complicated, since it isnecessary, in order to carry out the different method steps, to hold thepreform or the preform that has already been shaped, in part, indifferent workpiece holders, one after the other, so that a continuousshaping process is not possible. Furthermore, complicated adjustment isnecessary when changing the workpiece holder, so as to guarantee preciseconcentricity of the preform with the forming rollers. Furthermore, themethod is restricted to tubular preforms that can be elongated by meansof pressure rolling.

It is the task of the invention to develop such a method further in sucha manner that it allows a continuous method sequence and can be useduniversally.

This task is accomplished, in the case of a method of the type referredto initially, in that a tubular preform having a round or polygonalcross-section is used, and the preform is held in the center tube regionby one workpiece holder during the entire production process, until thehollow shaft is finished.

The method makes it possible to carry out the entire forming processwith only one workpiece holder, so that the entire forming process cantake place continuously. In this regard, additional adjustments are alsoeliminated, which would be necessary if the workpiece holder werechanged. Furthermore, it is possible to use tubular preforms having around (circular-ring-shaped) or polygonal cross-section, so that thehollow shaft produced in this manner is suitable for differentapplication purposes, for example for holding coil packages in the caseof an electric motor. During the shaping, in each instance, the preformis put into rotational movement relative to the at least one formingroller, for which purpose the workpiece holder with the preform and/orthe at least one forming roller is/are driven. During shaping, thepolygonal cross-section, for example, remains unchanged in the centertube region that is held by the workpiece holder, while only the endregions are shaped with rotation symmetry, so that the center region canhold coil packages of an electric motor, for example, without furthershaping. Since the center region is not shaped, an internal mandrel isnot required in the center region, either, but rather internal mandrelsare inserted only into the two end regions, while in the center region,the preform is held by a workpiece holder from the outside.

Both drawn and welded tubes can be used as a preform.

In a very particularly preferred embodiment, it is provided that the twoends of the preform are shaped simultaneously, at least in part. In thisway, on the one hand the shaping time is shortened, and on the otherhand this leads to torque neutralization in the center tube region.

Depending on the demands on the finished hollow shaft, it is preferablyprovided that at least one end is stepped once or multiple times, i.e.regions that border on one another axially are produced with differentdiameters.

Furthermore, it is advantageously provided that an outside and/or insideprofiling is introduced into at least one end.

In this regard, it is furthermore provided that before introduction ofthe outside and/or inside profiling, an internal mandrel, if necessary aprofiled one, is axially introduced into the at least one end.

If the finished hollow shaft is supposed to have an outside or insideprofiling on both ends, it is correspondingly provided that an internalmandrel is introduced into both ends, in each instance. For introductionof an outside profiling, at least one correspondingly profiled shapingroller and a non-profiled internal mandrel are used, and forintroduction of an inside profiling, at least one non-profiled shapingroller and a profiled internal mandrel are used.

It can very particularly preferably be provided that the two internalmandrels are connected with one another at their end faces, with forcefit and/or shape fit. The end face ends of the two internal mandrels canhave a spur gearing, for example, and are axially pressed against oneanother and thereby locked in place, so that lateral radial forces thatoccur can be absorbed.

Finally, it is advantageously provided that the shaping takes place, atleast part of the time, under the application of heat. The heat can beproduced inductively, for example, and, at the same time, hardening ofthe component can be achieved by means of this heat application.

In the following, the invention will be explained in greater detail asan example, using the drawing. This shows, in

FIG. 1 a longitudinal section through a tubular preform,

FIG. 2 a section along the line A-A in FIG. 1 with three differentembodiments,

FIG. 3 a perspective representation of the preform held by a workpieceholder in a center tube region, during shaping,

FIG. 4 a side view of FIG. 3, partly in longitudinal section,

FIG. 5 a longitudinal section through a finished hollow shaft,

FIG. 6 a detail X in FIG. 5,

FIG. 7 a detail Y in FIG. 5,

FIG. 8 a longitudinal section through a hollow shaft during shaping,using two separate internal mandrels,

FIG. 9 a modification of FIG. 8 with two internal mandrels connectedwith one another in the axial direction, with shape fit,

FIG. 10 a perspective representation of the two internal mandrelsaccording to FIG. 9,

FIG. 11 an end region of a preform, with a forming roller that applies aradial and axial force, and

FIG. 12 a perspective representation of FIG. 11.

A tubular preform is designated in FIG. 1 in general as 1. This tubularpreform 1 can be a drawn or welded tube made of metal. It is essentialto the invention that the tubular preform can have any desired round orpolygonal cross-section.

In FIG. 2, it is indicated, as an example, that it can have a circular,square or triangular cross-section. In general, any desiredcross-sectional shapes, preferably polygonal cross-sectional shapes, arepossible for adaptation to the purpose of use, in each instance.

Since the center tube region 1 a of the tubular preform 1 is not shapedin the case of the method according to the invention, this region issuitable without further processing for holding coil packages of anelectric motor or the like, for example.

In order to produce a hollow shaft from the tubular preform 1 by meansof pressure rolling, it is provided, as an essential part of theinvention, that the tubular preform is held in its center tube region 1a by a workpiece holder 2, during the entire production process up tothe finished hollow shaft. This divided, ring-shaped workpiece holder 2accordingly has an inside contour that corresponds to the outsidecontour of the tubular preform 1.

Since the preform 1 is held in its center region 1 a by the workpieceholder 2 during the entire production process, the entire methodsequence can take place continuously, without a change to a differentworkpiece holder.

Preferably, in this regard it is provided that the two ends 1 b and 1 cof the preform 1 are shaped simultaneously, at least in part, by meansof forming rollers designated in general as 3. In this regard, at leastone forming roller 3 is provided for shaping of each of the two ends 1b, 1 c. In the exemplary embodiment according to FIGS. 3 and 4, threeforming rollers 3 are indicated for shaping of the end 1 b, and oneforming roller 3 is indicated for shaping of the end 1 c.

The forming rollers 3 are configured to be radially displaceable withreference to the longitudinal axis 4 of the preform 1. Depending on thedesired shaping process, they can additionally also be displaceable inthe axial direction.

During shaping, the pressure rollers 3 are put into rotational movementrelative to the workpiece holder 2 and the tubular preform 1, so thateither the pressure rollers 3 or the workpiece holder 2 with the preform1 are/is driven.

By means of the shaping shown in FIGS. 3 and 4, the two ends 1 b and 1 cof the preform 1 are shaped with rotation symmetry, i.e. the two ends 1b and 1 c then no longer have a polygonal cross-sectional shape if theoriginal preform 1 had a polygonal cross-sectional shape. Of course, thepolygonal cross-sectional shape is maintained in the non-worked centerregion 1 a.

Proceeding from the tubular preform 1 that has already been shaped atthe two ends 1 b and 1 c, the two ends 1 b and 1 c can be shaped furtherwithout changing the workpiece holder 2.

In FIG. 5, it is shown that the two ends 1 b and 1 c are configured withtwo steps, in each instance, viewed in the radial direction. Thesestepped regions are indicated as 1 b′, 1 b″ and 1 c′, 1 c″,respectively, in FIG. 5. Furthermore, a profiling is introduced into thetwo ends 1 b and 1 c, in each instance, namely an inside profiling 5into the end 1 b and an outside profiling 6 into the end 1 c. The insideprofiling 5 and the outside profiling 6 can be a gearing, a knurling orsome other geometric shape.

Suitable shaping rollers are used as forming rollers and as internalmandrels to produce the inside profiling 5 and the outside profiling 6,respectively.

A further possible exemplary embodiment is shown in FIG. 8. The preform1 is held in the workpiece holder 2 in its center region la, without anychange, and an internal mandrel 7 without profiling is axiallyintroduced into the end 1 b that has already been stepped, while aninternal mandrel 8 having an outside profiling 8 a is introduced intothe end 1 c. In order to introduce an outside profiling 6 at the end 1 bof the preform 1 in the case of the exemplary embodiment according toFIG. 8, not only the internal mandrel 7 but also at least one formingroller 9 having an outside profiling 9 a is provided. On the other hand,in order to introduce an inside profiling 5 into the end 1 c of thepreform 1, not only the internal mandrel 8 having an outside profiling 8a but also at least one forming roller 10 without an outside profilingis provided, i.e. the end 1 c is pressed into the outside profiling 8 aof the internal mandrel 8 by the forming roller 10, so that the insideprofiling 5 is formed.

In contrast to the embodiment according to FIG. 8, in the case of theembodiment according to FIGS. 9 and 10, two separate internal mandrels 7and 8 are not used, but rather the two internal mandrels 7′ and 8′ areconnected with one another at the end faces and/or with shape fit. Forthis purpose, the two internal mandrels 7′ and 8′ have a complementaryend-face gearing 7 a, 8 a, in each instance. The internal mandrels 7′and 8′ are then pressed together in the axial direction during shaping,by means of pressure application from the outside, and thereby lateralradial forces that occur during shaping are absorbed.

It is also possible to feed metal material to at least one of the twoends 1 b, 1 c of the preform 1 during shaping (in the shaping zone), ifan axial force is applied to the end 1 b or 1 c, respectively. In thisregard, at least one forming roller 11 is used, which has a step-shaped,tubular outside circumference region having a circumferential contactsurface 11 a. An axial force F_(axial) and a radial force F_(radial) areexerted on the preform 1 with this forming roller 11. This material feedcan also be carried out multiple times, for example before the actualshaping of the ends 1 b, 1 c and afterward.

The entire production process can take place solely by means of coldforming. However, shaping can also take place while heat is applied, allof the time or part of the time, for example by means of inductive heatgeneration. In this way, hardening of the preform 1 can take place atthe same time.

REFERENCE SYMBOL LIST

-   1 tubular preform-   1 a center tube region-   1 b, 1 c ends-   1 b′, 1 c′ stepped region-   1 b″, 1 c″ stepped region-   2 workpiece holder-   3 forming rollers-   5 longitudinal axis-   6 inside profiling-   7 outside profiling-   7, 7′ internal mandrel-   8, 8′ internal mandrel-   8 a outside profiling-   8 b end-face gearing-   9 forming roller-   9 a outside profiling-   9 b end-face gearing-   10 forming roller-   11 forming roller-   F_(axial) axial force-   F_(radial) radial force

1. A method for the production of a hollow shaft from a tubular preformby means of pressure rolling, wherein the two ends of the preform areshaped using at least one forming roller, in each instance, wherein atubular preform (1) having a round or polygonal cross-section is used,and the preform (1) is held in the center tube region (1 a) by oneworkpiece holder (2) during the entire production process, until thehollow shaft is finished.
 2. The method according to claim 1, wherein adrawn or welded preform (1) is used.
 3. The method according to claim 1,wherein the two ends (1 b, 1 c) of the preform (1) are shaped at thesame time, at least in part.
 4. The method according to claim 1, whereinat least one end (1 b, 1 c) is stepped once or multiple times.
 5. Themethod according to claim 1, wherein an outside and/or inside profiling(5, 6) is introduced into at least one end (1 b, 1 c).
 6. The methodaccording to claim 5, wherein before introduction of the outside and/orinside profiling (5, 6), an internal mandrel, if necessary a profiledone (7, 7′, 8, 8′), is axially introduced into the at least one end (1b, 1 c).
 7. The method according to claim 6, wherein an internal mandrel(7, 7′, 8, 8′) is introduced into both ends (1 b, 1 c), in eachinstance.
 8. The method according to claim 7, wherein the two internalmandrels are connected with one another at their end faces, with forcefit and/or shape fit.
 9. The method according to claim 1, wherein theshaping takes place, at least part of the time, under the application ofheat.